Dropbox Makes Files Available To Law Enforcement. Is a Warrant Needed?

While up late with the baby one night recently, I came across a discussion on Dropbox providing information to law enforcement. 

The claim is:

"As set forth in our privacy policy, and in compliance with United States law, Dropbox cooperates with United States law enforcement when it receives valid legal process, which may require Dropbox to provide the contents of your private Dropbox," . Furthermore: "In these cases, Dropbox will remove Dropbox's encryption from the files before providing them to law enforcement." 

The unanswered question is what type of valid legal process is required.  One possibility is that Dropbox will provide files in response to a subpoena, which the government can easily issue in most investigations.  The other possibility is that Dropbox would require a warrant before providing the information.

Whether a warrant is needed turns on whether there is a reasonable expectation of privacy in files stored on Dropbox.  On the one hand, by uploading files on Dropbox, people are taking a risk that the files may be disclosed.  This is because the user is voluntarily providing the files to a third party.  On the other hand, by encrypting the files and requiring a password to access some of them, users may have a much greater expectation of privacy than in files that are made publicly available.

As noted here, some courts have held that the government must obtain a warrant before accessing emails stored by third parties.  The question for some court will be whether this rule applies to services like Dropbox.